"Reactive dyes" are colored compounds which have suitable groups capable of forming covalent bonds between a carbon atom of the dye ion or molecule and an oxygen, nitrogen or sulphur atom of a hydroxy, an amino or a mercapto group, respectively, of the substrate. "Cellulose reactive dyes" are based on a discovery made in 1954 by Rattee and Stephen, who claimed that, by applying water-soluble dyes containing a dichlorotriazine group to cellulose from a neutral dyebath and then increasing the pH value, covalent bonds were formed between a triazine carbon atom and an oxygen atom of a cellulose hydroxyl group. It was later found that monochloro triazine dyes also could be used as reactive dyes for cotton when the dyeing temperature and the pH value of the dyebath for the second part of the batch dyeing operation were increased. Since the original "cellulose reactive dyes" were discovered, other reactive groups have been discovered.
A typical "cellulose reactive dye" has the symbolic formula: ##EQU1## wherein RG is the reactive group, B is a bridge link, D is the chromagen, and W is a water solubilizing group. It is believed that the "cellulose reactive dyes" react strongly with primary hydroxyl groups of polymeric polysaccharides such as cellulose. Generally the reactive group is a halide radical and the by-product of the reaction is a hydrogen halide. Other reactive groups such as sulphuric acid ester groups of .beta.-hydroxyethylsulphone are also known. "B" shown above as a bridge link is found in many dyes but not in others and is therefore an optional link. In dyes where there is no bridge link, the reactive group is attached directly to the chromophoric system.
Illustrative of a specific "cellulose reactive dye" is a dye from the dichlorotriazine group having the formula: ##STR1##
The chloride radicals are the reactive groups RB. The triazine molecule is the bridge link. The --SO.sub.3 Na group is the water solubilizing group. The remainder of the molecule is the chromagen.
Below are shown a typical list of reactive and binder groups used in "cellulose reactive dyes":
Di- or mono-chlorotriazines PA1 2,4,5 trihalogenopyrimidine PA1 2-methylsulphonyl-4-methyl-5-chloropyrimidine PA1 3,6-dichloropyrazine PA1 2,3-dichloroquinoxaline PA1 2-chlorobenzthiazole PA1 4,5-dichloropyridazone PA1 (1) Print-dye-steam-wash PA1 (2) Print-dry-bake-wash PA1 (3) Print-dry-cold alkali solution-flash-age-wash PA1 (4) Print-dry-hot alkali solution-wash.
Dyes such as these react with textiles including cotton, wool, silk and nylon. The printing of textiles requires the dye solution to be thickened to produce good printing characteristics. After the textile is printed, the dye is set onto the fabric and the thickener is washed out of the fabric. Traditionally, "cellulose reactive dyes" are thickened with sodium alginate.
Sodium alginate does not have any primary hydroxyl groups with which the dye can react. Galactomannan and cellulose derivatives have primary hydroxyl groups with which the "cellulose reactive dyes" react. Because the dyes react with galactomannan and cellulose derivatives, these materials cannot be used as thickeners for this type of dye. The reaction between the thickener and the dye impairs the washing of the thickener from the textile. If the thickener is not washed out of the fabric, the fabric will be stiff or have a "harsh hand."